Alkylating agents are a major class of cancer chemotherapeutic compounds. Many clinically used alkylating agents are bifunctional compounds having two chemically reactive centers capable of reacting with and cross-linking biomolecules, such as the opposite strands of duplex DNA. Use of these agents to alkylate biomolecules may lead to a variety of defects in intracellular metabolism, particularly defects in nucleic acid replication and/or transcription, which tend to be more lethal in rapidly growing cancer cells than in normal somatic cells. Busulfan is a bifunctional alkylating agent which is commonly used in the treatment of leukemias. Busulfan is a linear methanesulfonic ester of 1,4-butanediol which functions by forming a butane cross-link between a pair of nucleophiles, such as the 7-position guanine nitrogens in opposite strands of duplex DNA. Initial nucleophilic attack at one of the butane end-carbons in the compound releases a negatively charged methanesulfonic acid group, leaving an uncharged methanesulfonic ester of 1-butanol attached to the nucleophile. A second nucleophilic attack on the opposite butane end-carbon results in cross-linking through the butane moiety, and release of a second negatively charged methanesulfonic acid group. Busulfan is more effective therapeutically than other linear disulfonic esters having cross-linking alkane moieties, which are either shorter or longer than butane.
U.S. Pat. No. 4,950,768 discloses cyclic disulfonic esters having the general structural formula:

Where m=0 or 1, n=1-5, and R=H, CH3, CH3CH2 or Cl. These compounds can be used as bifunctional agents for cross-linking a variety of nucleophile-containing biomolecules, such as proteins and nucleic acids. The disclosure includes references that cyclic disulfonic ester in which m=0, n=2 and R=H, (i.e., ethylene methanedisulfonate) is effective in the treatment of a variety of mice cancers, including lymphocytic leukemia, lymphoid leukemia, melanocarcinoma, human breast xenograft and ovarian carcinoma. Cyclic disulfonic esters in which m=0, n=3 or 4 and R=H have also been shown to have anti-leukemia activity.
Unlike uncharged linear alkane disulfonates such as Busulfan, initial nucleo attack on a cyclic diester compound in opening the diester ring, results in a linear sulfonate having a charged sulfonic acid end-group which remains attached to the compound. The charged group has the capacity to affect both the solubility of the compound and its configuration in relation to the alkylated biomolecule, in the period between the two nucleophilic cross-linking reaction events.
The mechanism by which ethylene methane disulfonate alkylates DNA has been studied by Gibson, Hartley and Kohn, Cancer Research, 46, 1679-1683, April 1986. Their work has disclosed that the mechanism of reaction of this alkylating agent is not at all like that of Busulfan and other alkylating agents, which cross-link DNA strands via alkylation of the guanine moiety. Instead, ethylene methanedisulfonate cross-linking appears to occur via phosphate ester alkylation followed by linkage of these strands to protein. This is most likely histones, since the first alkylation step produces a negatively charged intermediate, i.e., —SO3—, and histones, which enfold DNA, are positively charged.